1. Field of the Invention
The present invention relates to a 3D (three dimensional) image displaying method for a 3D image displaying apparatus which produces a parallax at least in one direction, and such a 3D image displaying apparatus.
2. Description of the Related Art
A 3D image displaying method without the need for special viewing glasses includes stereo-view and multi-view types. In both type systems, a lenticular sheet (array of semicircular lenses that have a lens property in a horizontal direction only) or a parallax barrier is provided on the display surface, and 2D information that includes a parallax is presented independently to the left and right eyes. The viewer thereby perceives a 3D image.
With the stereo-view system, two pieces of 2D information is offered so that a viewer perceives a 3D image from a viewpoint in a single direction. With the multi-view system, four pieces of 2D information are used, for example, so that a viewer perceives a 3D image from viewpoints in three directions. In other words, a phenomenon called motion parallax in which an object moves in a direction opposite to the motion of the body is presented to the viewer, although the movement of the object is not continuous.
Integral imaging (II) is a system that makes improvements in the motion parallax and displays a 3D image that involves the motion parallax. This system is based on a system called integral photography (IP) for taking and reproducing a 3D photograph, which was proposed on 1908 (e.g., M. G. Lippmann, Comptes Rendus de l'Academie des Sciences, Vol. 146, pp. 446-451 (1908), IP). In this system, a lens array that corresponds to pixels of a 3D photograph is prepared, and photographing is conducted with a film placed at the focal length of the array. When reproducing, the lens array that is used for photographing is placed on the film.
The process of reproducing the optical information recorded through a lens only by reversing the proceeding direction means that it does not limit the viewing position. Moreover, if the resolution of the film is sufficient enough, a perfect aerial image can be reproduced in a similar manner to holography. Thus, the II system is an ideal system. A 3D image displaying apparatus of the II system adopts a liquid display (LCD), which is a common flat panel display, in place of film.
The course of the light emitted from the pixels is regulated so that the light is projected as a beam. As the number of pixels behind the lens increases, or in other words the number of pieces of parallax information (image information that changes in appearance depending on the view angle) increases, the display range in front of or the back of the 3D image displaying apparatus becomes larger. However, the resolution of the 3D image is lowered under a condition that the resolution of the LCD is unchanged, because the lens pitch is increased (e.g., H. Hoshino, F. Okano, H. Isono, and I. Yuyama, J. Opt. Soc. Am. A., Vol. 15, pp. 2059-2065 (1998), NHK).
The II system is featured in that the number of parallaxes is increased to the extent possible, while giving consideration to the decreasing fineness of the viewpoint image. Moreover, the position of the viewer is not limited when designing the beaming system (i.e., the light focusing points are not specially arranged at the positions of the viewer's eyes). This clearly differentiates the II system from the multi-view system, where 3D image perception is realized by setting the number of parallaxes to two to four to prevent the fineness of the viewpoint image from being lowered, and providing the light focusing points at positions corresponding to the eyes of the viewer.
More specifically, the horizontal lens pitch or an integral multiple of the horizontal lens pitch is designed to match an integral multiple of the horizontal pixel pitch. This makes the beams projected from the lenses substantially parallel to one another so that the beams would not gather at a certain point in the reproduction and observation space. Otherwise, a method may be adopted, with which the light focusing point is designed far beyond the viewing distance. These beams are reproduced, based on the discretely extracted light that was given out from the surface of the object that really existed there. Thus, if a large number of parallaxes are provided, the viewer can perceive a binocular viewpoint image within the viewable range that should be seen from around the viewer's position. Furthermore, continuous motion parallax can be obtained.
In essence, the only difference between the 1D-II and multi-view systems resides in the restriction on the layout of beams due to the limited number of pixels of a flat panel such as an LCD. Unlike the multi-view system, however, in which emphasis on the fineness of the viewpoint image results in incomplete motion parallax, the 1D-II system that does not have any specific light focusing point offers a more natural and less tiring 3D image in which binocular parallax and motion parallax are well balanced.
However, there is a restriction on the display in the depth direction of the 3D image displaying apparatus of each type. First, in the 3D image displaying apparatus of the II system, the display is limited in its depth direction because the distance between pieces of the parallax information that are presented becomes larger as the viewer is situated farther away from the display surface (e.g., H. Hoshino, F. Okano, H. Isono, and I. Yuyama, J. Opt. Soc. Am. A., Vol. 15, pp. 2059-2065 (1998), NHK). As for the multi-view system, the 3D image could be multiplexed if multiple pixels are simultaneously viewed through the lenses. To avoid this, a restriction should be placed on the depth of the display to the extent similar to the II system. For the stereo-view system, there is a restriction on the depth of the display to solve the problem of fatigue caused by incoherence of vergence accommodation. In other words, whichever display system is chosen, the display range is limited to plus or minus several centimeters. To present a realistic 3D image in the limited display range, a flatbed-type display may be adopted.
In comparison to the upright type, the flatbed type can shorten the distance from the 3D image displaying apparatus to the viewer without making the viewer aware of this. To the human's eyes, 10 centimeters in immediate proximity presents more spatial effect than 10 centimeters at a distance. The flatbed type, which is positioned closer to the viewer, can bring about excellent spatial effect.
In addition, the 3D image displaying apparatus of the flatbed type situated in such a manner that the viewer looks down at it has a display range that corresponds to the area where manual works are performed. It is reported that, when handling an object, a human subconsciously uses body parts of one's own, such as the palm, as a reference size. The average male's palm is about 9 centimeters wide. This means that an approximately 10-centimeter-high 3D image within a manual work range would bring about sufficient spatial effect.
Furthermore, as can be seen from objects on a desk, an object that is floated above the reference plane or an object extremely tall with respect to the floor area tend to be limited.
In addition, a human seems to focus on projections and depressions more on the lower side than in front. It is considered that evolution of any creature proceeds in a direction of obtaining information that means more to the self at a higher sensitivity. It is assumed that, in the history of human beings, vertical projections and depressions such as those at hand when performing hand works and those under one's feet, which may lead directly to toppling, misstep, and other accidents, have meant more than horizontal projections and depressions.
For the above reasons, a human seems to have a higher sensitivity toward vertical projections and depressions than toward horizontal projections and depressions, and thus it can be assumed that a flatbed-type device increases the value of stereoscopic information and improves the impact of a 3D image.
In addition, a flatbed-type or almost-flatbed-type 3D image displaying apparatus that displays 2D information such as characters and icons, as well as 3D images, has been suggested (e.g., Japanese JP-A 2001-331169 (KOKAI)).
The 3D image displaying apparatus with its display surface designed to be substantially horizontal can display a 3D image that has spatial effect. It is preferable for the device to be capable of more effectively and impressively displaying 2D information as well.